1. Field of Invention
The present invention relates to liquid crystal substrates and reflective-type liquid crystal panels using the substrate, and in particular, relates to a technique that can preferably be applied to active-matrix liquid crystal panels in which pixel electrodes are switched by switching elements formed on the substrate. Furthermore, the present invention relates to electronic equipment and projection type display devices both using the liquid crystal panel.
2. Background of Related Art
Conventionally, as active-matrix liquid crystal panels used for light valves of projection type display devices, liquid crystal panels having a thin film transistor (TFT) array, employing amorphous silicon, on a glass substrate as switching elements of pixels have been put into practical use.
Active-matrix liquid crystal panels using the above TFTs have low TFT element mobility and a large device size. Thus, for example, a projection type display device, such as a projector, equipped with the liquid crystal panel as a light valve, is disadvantageously large in size. Furthermore, transmissive-type liquid crystal panels have the following fatal disadvantage: the aperture ratio decreases as the resolution of the panel increases, such as XGA or SXGA, since the regions of the TFTs provided for every pixel do not transmit light.
As compared with the transmissive-type active-matrix liquid crystal panels, reflective-type active-matrix liquid crystal panels are small in size and have an insulated gate field effect transistor (MOSFET) array formed as switching elements on a semiconductor substrate so as to control the voltage applied to pixel electrodes which are to be used as reflective electrodes.
As is mentioned above, in active-matrix liquid crystal panels having transistor elements formed on a glass or semiconductor substrate, when light leaks through spaces formed between the pixel electrodes, hole-electron pairs are generated in a PN junction (e.g., a junction between source/drain regions and a channel region of the transistor, or a junction between source/drain regions and a well) of the semiconductor layer or semiconductor substrate, so that a light leakage current flows and undesirably destabilizes the electric potential of the semiconductor layer, the semiconductor substrate, or the well. In the case of reflective-type liquid crystal panels, the amount of light leakage can be reduced as compared with that of the transmissive type by, for example, forming the pixel electrodes close to each other in the top layer without using particular light-shielding means. However, in reflective-type liquid crystal panels used for light valves of projection type display devices, strong light is converged and is incident on the spaces between the pixel electrodes. Thus, it is not sufficient to arrange the pixel electrodes close to each other to avoid the light leakage current.
In particular, since liquid crystal panels with a semiconductor substrate have well regions, the leaking light transmitted through not only the transistor portion but also the portion at a certain distance from the transistor portion may cause a light leakage current. Therefore, unless sufficient countermeasures are taken, the light leakage current increases as compared with liquid crystal panels having TFTs as switching elements on a glass substrate.
Furthermore, in active-matrix liquid crystal panels having transistor elements on a glass or semiconductor substrate, peripheral circuits such as a scanning side driving circuit and a data line driving circuit are formed on the same substrate; there is a problem such that the light leakage current is generated and the peripheral circuits are operated by mistake when light enters to such peripheral circuits.
Moreover, in reflective-type liquid crystal panels, an insulating film is exposed by the spaces between the pixel electrodes, and the light reflected by the surface of the insulating film changes its direction by 180° and emerges. As a result, the emerging light is displayed as unwanted light, which deteriorates the quality of the image.